The extensible markup language (XML) is a language that is written in the standardized general markup language (SGML). SGML is an international standard meta-language for text markup applications (ISO 8879). XML is a human-readable, text-based language making it easy to use. Partly because XML is written in an international standard and partly because of its ease of use, XML is widely used in a variety of applications. Another advantage is that XML files or documents explicitly flag the type of data contained in the documents by enclosing blocks of data with labels to declare the type of XML elements contained in a block. This makes XML documents data-type aware.
However, because it is human-readable and because it is data-type aware, XML can be a verbose language. Human-readable data files are larger compared to other formats (such as binary formats for example) and the data-type declarations expand the size of data files. Large XML files may cause problems in systems that are memory constrained or in communication systems having channels that are bandwidth limited.